The effectiveness of fish ladders can be debated, but that hasn’t stopped a few professors at South Dakota State University from designing some to help fish in their state.
Over last summer, they worked to test the effectiveness of their ladder design for aiding fish passage. The researchers installed a number of the ladders in eastern South Dakota and the Black Hills area.
According to a release from the university, the layout of the fish ladders is meant to mostly help small-bodied fish as larger, bottom-dwelling swimmers are the only ones that have had difficulty passing through.
Scientists made that determination through testing the fish ladders at 19 sites — nine in eastern South Dakota and 10 in western South Dakota, particularly in the Black Hills. The ladders were deployed in culverts that ranged from 2 to 12 feet in diameter with the drop-off distance from culvert lip to the streams below ranging from 8 inches to 60 inches.
Statewide, 23 species of small fish passed through the ladders during the study period. The average passage rate for ladders in eastern South Dakota was more than 28 fish per day, while it was 1.2 fish per day in West River. Researchers say that could be explained by lower stream temperatures in the Black Hills region that seem related to lower fish numbers.
They are hopeful that the fish ladders can help to reduce habitat fragmentation for sport fish in the state. Fragmentation of habitat for native and introduced sport fish is a concern for wildlife managers, because the ability to pass through culverts would improve fisheries management by increasing the amount of habitat available to fish.
Some of the fish common at sites where the fish ladders were tested include grazing minnows, like Central Stonerollers. These fish feed on algae from rocks and logs on the bottom of the stream, which helps to mitigate the impacts of agricultural runoff and algae.
As adults, these small-bodied fish often move up- and downstream, traveling from 1 to 2 miles in a day, to find better areas to spawn and feed. This movement upstream, followed by a gradual migration back downstream, is important for stable population numbers as minnow offspring often stay in the small, shallow headwaters until they’re big enough to survive in deeper, faster waters.
The researchers field-tested the ladders through a $112,086 grant from the South Dakota Department of Game, Fish and Parks. The fish ladder project was also supported by U.S. Department of Agriculture Hatch funds through the South Dakota Agricultural Experiment Station.